1. Field of the Invention
The present invention relates generally to devices for removing contaminants from a gas or vapor stream and, more particularly, to a moving granular bed filter for removing contaminants from a gas or vapor stream.
2. Description of the Related Art
The removal of contaminant materials from a gas or vapor stream is required in numerous diverse applications. For instance, fly ash must be removed from the exhaust gas stream of a coal-fired powerplant in order to meet applicable pollution regulations. As another example, sulfur dioxide gas is also preferably removed from the same exhaust stream from the coal-fired powerplant. Other examples include any process in which a gas or vapor reacts with a solid, such as in a fluidized bed reaction vessel of a chemical process or in a catalytic process at a petroleum refinery. In short, numerous processes and applications involve the undesirable entrainment of a particulate or other contaminant within a gas or stream, which contaminant is preferably removed for various purposes. Among the purposes for which entrained contaminants are removed from a gas stream include the meeting of environmental regulations concerning the contaminants borne in an exhaust gas stream, the recovery of gas-borne materials for sale or reuse, as well as for other purposes.
Among the known devices employed in removing contaminants from a gas or vapor stream are the electrostatic precipitator (ESP), the cyclone device which operates as a centrifuge, and the bag house. While these three device can be operated either at low pressures or high pressures, such devices typically can operate only at relatively low temperatures. The requirement of low temperature operation limits the applicability of these devices inasmuch as numerous chemical processes and power generation operations involve high temperature applications.
Another contaminant removal device is the moving granular bed filter, which employs a moving bed of granular media to remove contaminants from a gas or vapor stream. Such moving granular bed filters have been successfully employed in high temperature, high pressure applications. Nevertheless, the cost of such moving granular bed filters has been relatively high since the vessels most typically are of a cylindrical configuration to withstand the high pressures involved in the application. It is thus desired to provide a moving granular bed filter suitable for use in high temperature, low pressure applications and that can be economically manufactured.
Since moving granular bed filters operate by capturing or trapping gas or vapor-borne contaminants within the granular media, it is understood that such filter a typically cannot remove 100% of any given contaminant in one filtering operation and, depending upon the application, it is thus often necessary to pass the gas through multiple moving granular bed filters that may employ different granular media or the same type of granular media but of a different particle size to progressively remove incremental amounts of the contaminants from the gas stream. It is thus desired to provide a moving granular bed filter that can easily be connected in a series and/or parallel relation with other such moving granular bed filters in a filtration operation.
Since the granular media and the gas stream typically are both moving simultaneously through the vessel of the moving granular bed filter, different filtration effects can be achieved depending upon whether the granular media and the gas stream are moving together in generally the same direction (concurrent flow) or are moving against one another in opposite directions (counter-current flow). It is thus desired to provide a moving granular bed filter that can induce both concurrent and counter-current flow in the same vessel in order to maximize capture of the contaminants from the gas or vapor stream.
In accordance with the foregoing, a moving granular bed filter for removing contaminants from a gas or vapor stream employs a quantity of granular media that is passed through a vessel while the contaminant-laden gas stream is passed through the granular media to remove at least a portion of the contaminants from the gas stream and into the granular media. The vessel includes a media inlet that extends between a pair of opposite regions of the vessel and delivers the granular media into the interior of the vessel such that the granular media forms a freely-formed pile within the interior of the vessel to defame first and second chambers above the upper surface of the pile and on opposite sides of the media inlet. In one embodiment, the media inlet is disposed at the lower end of a media delivery channel that extends downwardly into the interior of the vessel and which supplies the granular media to the media inlet. In the same embodiment, the vessel additionally includes a gas flow direction plate disposed within the media and extending between the pair of opposite regions of the vessel to direct the flow of the gas stream both concurrent and then counter-current with the flow of the granular media through the vessel. In another embodiment, the vessel does not include the gas flow direction plate. In still another embodiment, the media delivery channel may include a flared skirt that forms the media inlet.
An objective of the present invention is to provide a reduced-cost moving granular bed filter.
Another objective of the present invention is to provide a moving granular bed filter that can be employed in high temperature applications.
Another objective of the present invention is to provide a moving granular bed filter that can be employed in low pressure applications.
Another objective of the present invention is to provide a moving granular bed filter that can be constructed inexpensively by manufacture primarily out of common channel and plate members and that generally does not require special fabrication techniques apart from welding.
Another objective of the present invention is to provide a moving granular bed filter in which multiples of the filter can easily be connected in a series and/or parallel configuration.
Another objective of the present invention is to provide a moving granular bed filter in which the gas stream experiences both concurrent and counter-current flow with respect to the movement of the granular media through the vessel.
Another objective of the present invention is to provide a moving granular bed filter that employs a pile of granular media which can be configured to provide in various degrees both concurrent and counter-current flow of the gas stream with respect to the moving granular media.
An aspect of the present invention thus is to provide a moving granular bed filter for removing contaminants from a gas stream with a quantity of granular media, the general nature of which can be stated as including a vessel having a wall structure and being formed with a hollow interior, with the vessel including a gas inlet, a gas outlet, a media inlet, and a media outlet in communication with the interior. In such a moving granular bed filter, the media inlet extends between a pair of opposed regions of the wall structure and is structured to supply the granular media to the interior of the vessel. The granular media forms in a freely-formed filtration pile within the interior of the vessel, with the filtration pile having an upper surface, and the filtration pile extending between the media inlet and the media outlet and extending between the pair of opposed regions of the wall structure to define a first chamber and a second chamber within the interior. The first and second chambers each extend from the upper surface of the filtration pile, with the first chamber extending between a first side of the media inlet and the wall structure, and the second chamber extending between a second opposite side of the media inlet and the wall structure. The gas inlet is in communication with the first chamber, the gas outlet is in communication with the second chamber, and the filtration pile of granular media is operatively interposed between the first and second chambers.
Another aspect of the present invention is to provide a moving granular bed filter for removing contaminants from a gas stream with a quantity of granular media, the general nature of which can be stated as including a vessel having a wall structure and a roof connected with one another, and the vessel being formed with a hollow interior defined between the wall structure and the roof. The vessel includes a gas inlet, a gas outlet, a media inlet, and a media outlet in communication with the interior. The vessel further includes a media delivery channel extending partially into the interior of the vessel and terminating at the media inlet, the media delivery channel including a first media direction plate and a second media direction plate that each extend between a pair of opposed regions of the wall structure. The media inlet is structured to supply the granular media from the media delivery channel to the interior of the vessel to form a freely-formed filtration pile within the interior of the vessel, the filtration pile having an upper surface and extending between the media inlet and the media outlet and between the pair of opposed regions of the wall structure to define a first chamber and a second chamber within the interior. The first and second chambers each extend from the upper surface of the filtration pile, with the first chamber extending between the first media direction plate and the wall structure, and the second chamber extending between the second media direction plate and the wall structure. The gas inlet is in communication with the first chamber, the gas outlet is in communication with the second chamber, and the filtration pile of granular media is operatively interposed between the first and second chambers.
Still another aspect of the present invention is to provide a method of removing contaminants from a gas stream using a quantity of granular media within a moving granular bed filter, the general nature of which can be stated as including the steps of maintaining a freely-formed filtration pile of the granular media within the interior of a vessel of the moving granular bed filter, flowing the gas stream including the contaminants from the exterior of the vessel through a gas inlet into a first chamber, passing the gas stream through the filtration pile to remove at least a portion of the contaminants from the gas stream, and discharging the gas stream into a second chamber and through a gas outlet to the exterior of the vessel. In employing such a method, the filtration pile extends between a pair of opposed regions of a wall structure of the vessel and between a media inlet and a media outlet to define the first and second chambers within the interior of the vessel. The first and second chambers each extend upwardly from the upper surface of the filtration pile on opposite sides of the media inlet, and the media inlet and the media outlet are in communication with the exterior of the vessel.